This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Background: The development of the intestinal microbiota is influenced by factors such as age, diet, and environment. There is limited data on intestinal bacterial colonization among hospitalized premature infants. Objectives: The study aims to describe and compare the development of intestinal microbiota among hospitalized premature infants receiving different types of milk. Methods: Neonates weighing 1000-1500 grams admitted to Texas Childrens Hospital Neonatal Intensive Care Unit (TCH NICU) within the first forty-eight hours from birth will be enrolled in the study. Neonates with congenital anomalies and perinatal asphyxia will be excluded. There will be three groups of neonates namely: expressed breast milk group, donor milk group and the formula milk group. Stool samples will analyzed for types of bacteria and relative amounts of bacteria over a period of six weeks. Expressed breast milk will be evaluated for presence of bacteria with probiotic potential and for pathogen. The occurrence of co-morbidities such as feeding intolerance, early and late onset sepsis and necrotizing enterocolitis will be compared among the three groups.